ES2449475T3 - Digital watermark generator, digital watermark decoder, method to provide a digital watermark signal in dependence on binary message data, method to provide binary message data in dependence on a digital watermark signal and computer program that uses differential coding - Google Patents

Abstract

Watermark generator (101; 2400) for supplying a watermark signal (101b; 2420) based on binary message data (101a, m; 2410), the watermark generator comprising: an information processor ( 303, 304, 305; 2430) configured to distribute the binarious message data a plurality of frequency bands or frequency subbands and to provide, based on information units of the binary message data, a first representation in the azitotemporal-frequency (b (ij); 2432) whose values represent binary message data for a plurality of frequency bands or sub-bands of frequencies and time blocks, where b (i, j) is the bit for the i -th frequency band or sub-frequency band and the jth time block; and a differential encoder (306; 2440) configured to derive a second representation in the field-time-frequency (306a, bdiff (i, j); 2442) of the first representation in the time-frequency field, so that the second representation in the temporal-frequency scope comprises a plurality of values, where a bdiff value (i, j) of the second representation in the temporal-frequency scope is a function of a bdiff value (i, j-1) of the second representation in the temporal-frequency field and of a value b (i, j) of the first representation in the temporal-frequency scope and where a difference between two values (bdiff (i, j), bdiff (i, j-1)) of the second representation in the scope temporal-frequency represents a corresponding value of the first representation in the temporal-frequency scope, to obtain a differential codification of the values of the first representation in the temporal-frequency field; and a watermark signal provider (307; 2450) configured to deliver the watermark signal based on the second representation in the time-frequency scope.

Description

Digital watermark generator, digital watermark decoder, method to provide a digital watermark signal in dependence on binary message data, method to provide binary message data in dependence on a digital watermark signal and computer program that uses differential coding

Technical Field

[0001] The modalities according to the invention relate to a digital watermark generator to provide a digital watermark signal depending on binary message data. Additional embodiments according to the invention refer to a digital watermark decoder to provide binary data of messages depending on a watermark signal. Additional embodiments according to the invention relate to a method of providing a digital watermark signal in dependence on binary message data. Additional modalities according to the invention relates to a method for providing binary message data in dependence on a watermark signal. Additional modalities are related to the corresponding computer programs.

[0002] Some embodiments according to the invention relate to a robust digital watermarking system of low complexity audio.

Background of the Invention

[0003] In many technical applications, it is desired to include additional information in a signal representing useful information or data or "main data" such as an audio signal, a video signal, graphics, a measurement amount and so on. In many cases, it is desired to include the additional information such that the additional information is linked to the main data (for example, audio data, video data, still image data, measurement data, text data, etc.) in a form that is not perceptible by a user of the mentioned data. Also, in some cases it is desirable to include additional data such that the additional data is not easily removable from the main data (eg, audio data, video data, still image data, measurement data, and so on).

[0004] This is particularly true in applications where it is desirable to implement digital rights management. However, sometimes it is desired to simply add substantially imperceptible side or secondary information to useful data. For example, in some cases it is desirable to add lateral information to the audio data, such that the lateral information provides information about the source of the audio data, the content of the audio data, the rights related to the data. of audio and so on.

[0005] To embed additional data in useful data or "main data", a concept called "digital watermark" can be used. Watermark concepts have been discussed in the literature for very different types of useful data, such as audio data, still image data, video data, text data and so on.

[0006] Next, some references will be given where the concepts of watermarks are discussed. However, the reader's attention is also directed to the vast field of textbook literature and publications related to digital watermarks for more details.

[0007] DE-196 40 814 C2 describes a coding method for the introduction of a non-audible data signal in an audio signal and a method for decoding a data signal, which is included in an audio signal in a non- audible. The coding method for the introduction of a non-audible data signal into an audio signal comprises the conversion of the audio signal into the spectral domain. The coding method also comprises determining the masking threshold of the audio signal and providing a pseudo noise signal. The coding method also comprises providing the data signal and multiplying the pseudo noise signal with the data signal, in order to obtain a frequency dispersion data signal. The coding method also comprises the weighting of the propagation data signal with the masking threshold and the superposition of the audio signal and the weighted data signal.

[0008] Furthermore, WO 93/07689 describes a method and apparatus for the automatic identification of a program broadcast by a radio station or by a television channel, or recorded on a medium, by adding an inaudible coded message. For the program's sound signal, the message identifies the channel or broadcast station, the program and / or the exact date. In an embodiment discussed in said document, the sound signal is transmitted through an analog-digital converter to a data processor that allows frequency components to be separated, and allowing energy in some of the frequency components to be altered in a predetermined manner to form an encoded identification message. The output of the data processor is connected by a digital-analog converter to an audio output for the broadcasting or recording of the sound signal. In another embodiment discussed in said document, an analog bandpass is used to separate a frequency band from the sound signal, so that the energy in the separate band can thus be altered to encode the sound signal.

[0009] The U.S. Patent No. 5,450,490 describes an apparatus and methods for the inclusion of a code that has at least one code frequency component in an audio signal. The capabilities of the various frequency components in the audio signal to mask the code frequency component for human hearing are evaluated and on the basis of these evaluations an amplitude of the code frequency component is assigned. Methods and apparatus for detecting a code in an encoded audio signal are also described. A code frequency component in the encoded audio signal is detected on the basis of an expected amplitude of code or on a noise amplitude within a range of audio frequencies, including the frequency of the code component.

[0010] WO 94/11989 describes a method and apparatus for encoding / decoding broadcast or recorded segments and monitoring the audience's exposure thereto. Methods and apparatus for encoding and decoding information on broadcasts or recorded segment signals are described. In an embodiment described in the document, an auditorium monitoring system encodes identification information in the audio signal portion of a broadcast or a segment recorded using expanded spectrum coding. The monitoring device receives an acoustically reproduced version of the broadcast or signal recorded by a microphone, decodes the identification information of the audio signal portion despite significant ambient interference and stores this information, automatically providing a diary for the member of the auditorium, which is then loaded to a centralized installation. A separate monitoring device decodes additional information from the broadcast signal, which is coupled with the daily auditorium information in the central facility. This monitor can simultaneously send data to the centralized installation using a dial-up telephone line, and receives data from the centralized installation through an encoded signal using an expanded and modulated spectrum technique with a third-party broadcast signal. part.

[0011] WO 95/27349 describes apparatus and methods that include codes in audio signals and decoding. An apparatus and methods for including a code that has at least one code frequency component in an audio signal is described. The capabilities of the various frequency components in the audio signal to mask the code frequency component to human hearing and based on these evaluations, an amplitude is assigned to the code frequency components. Methods and apparatus for detecting a code in an encoded audio signal are also described. A code frequency component in the encoded audio signal is detected based on an expected amplitude of code or an interference amplitude within a range of audio frequency components including the frequency of the code component.

[0012] DE 10 2008 014311 A1 describes a robust watermarking technique for embedding spectrum propagated watermarks in an audio data stream.

[0013] However, in the known digital watermark systems, reliability issues arise from the digital watermark or mark signal affected by a Doppler shift that can occur for example due to a movement of an apparatus receiving the digital watermark signal or in the case of a mismatch of local oscillators on the side of the digital watermark generator and on the side of the digital watermark stamp decoder.

[0014] In view of this situation, an object of the present invention is to create a digital watermark stamp concept and a digital watermark detection concept, which allows improved reliability in the case of a frequency shift. Doppler that affects the digital watermark signal or in the case that there is a frequency deviation between the local oscillators of the digital watermark generator and the digital watermark decoder.

Summary of the Invention

[0015] This object is achieved by a digital watermark or stamp generator according to claim 1, a digital watermark decoder according to claim 7 or 8, a method of providing a watermark signal digital depending on binary message data according to claim 13, a method for providing binary message data in dependence on a digital watermark signal according to claim 14 and a computer program according to claim 15.

[0016] An embodiment according to the invention creates a digital watermark generator to provide a watermark signal depending on binary message data. The watermark generator comprises an information processor configured to provide, depending on units of information (for example bits) of the binary message data, a first time domain-frequency representation, values of which represent the message data binary. The digital watermark generator also comprises a differential encoder configured to derive a second domain-frequency-time representation from the first domain-frequency-time representation, such that the second domain-frequency-time representation comprises a plurality of values, where a difference between two values of the second domain-frequency-time representation, represents a corresponding value of the first domain-frequency-time representation, to obtain a difference coding of the values of the first domain representation -frequency-time. The digital watermark generator also comprises a digital watermark signal provider configured to provide the digital watermark signal based on the second domain-frequency-time representation.

[0017] It is the idea of the present invention that a digital watermarked signal is particularly robust with respect to degradation, for example, by the Doppler effect, if adjacent domain-frequency-time values (for example associated with bands) adjacent frequency or bit intervals) are encoded such that a difference between the characteristics of these adjacent signal portions, these characteristics are represented by the values of the second domain-frequency-time representation, allows to conclude the corresponding value in a unique way of the first domain-frequency-time representation. In other words, the differential coding in the domain-frequency-time allows the generation of a robust digital watermark signal, for example by providing a domain-frequency-time audio signal, the audio content of the digital water of which is determined by the second domain-frequency-time representation.

[0018] In this way, improved robustness against movement and frequency inequality of the local oscillators is achieved by differential modulation. In fact, the Doppler effect, which is caused for example by a movement of a signal transducer that provides the digital watermarked audio signal to a digital watermark decoder, and frequency inequalities lead to a rotation of a modulation constellation, for example a Binary Phase Shift / Shift Coding constellation (BPSK = Binary Phase-Shift Keying). The harmful effect of this Doppler shift or frequency inequality can be reduced or completely eliminated by differential coding. In this way, differential coding has the effect that the digital watermarked signal, which is provided based on the second domain-frequency-time representation, is insensitive to a two-bit rotation in a complex plane.

[0019] In a preferred embodiment, the information processor is configured to provide the first domain-frequency-time representation, such that the values of the first domain-frequency-time representation represent the binary message data in The shape of a binary pattern. In this case, the differential encoder is configured to derive the second domain-frequency-time representation such that there is a phase change between two subsequent values of the second domain-frequency time representation if a corresponding value of the first domain representation- frequency-time takes a first value, and such that there is no phase change between subsequent values of the second domain-frequency-time representation if a corresponding value of the first domain-frequency-time representation takes a second value, which is different from A first value.

[0020] In a preferred embodiment, the digital watermarked signal provider is configured to provide an audio signal based on the second domain-frequency-time representation, such that a watermark frequency component digital of the digital watermarked signal comprises a uniform or staggered phase change in response to a first value of the first time domain-frequency representation, and such that a digital watermark frequency component of the digitally marked signal Digital water comprises a temporary constant phase in response to a second value of the first frequency-time representation, which is different from the first value.

[0021] In a preferred embodiment, the digital watermarked signal provider is configured to provide a first bit shaping waveform, in response to a first value of the second domain-frequency-time representation, and for provide a second bit shaping waveform, in response to a second value of the second domain-frequency-time representation. The digital watermark signal provider is configured to include a weighted or unweighted overlay of the time shifted versions of the same bit shaping waveform in response to the presence of a digital watermark signal. first value in the first domain-frequency-time representation, and to include in the digital watermarked signal a weighted or unweighted overlay of the time-shifted versions of a first bit shaping waveform and a second bit forming waveform, in response to the presence of a second value, which is different from the first value, in the first domain-frequency-time representation. This mode has the advantage that the sum (or superposition) of the time-shifted versions of the same bit shaping waveform can easily be distinguished from a sum (or overlap) of a first bit shaping waveform and a second bit forming waveform, if the bit forming waveforms are sufficiently different. As subsequent bit shaping waveforms are affected by a channel, whereby the digital watermarked signal is transmitted, in the same or at least approximately the same way it is simple to conclude the value of the first domain representation- frequency-time, due to the reception of two bit shaping waveforms (identical or approximately identical) allows the conclusion that the value of the first domain-frequency-time representation was in the first state (for example +1 ). Similarly, the reception of any two significantly different bit shaping waveforms allows the conclusion that the value of the first domain-frequency-time representation was in the second state (for example -1).

[0022] In a preferred embodiment, the second bit forming waveform is an inverse version of the first bit forming waveform. This allows to easily conclude the value of the first domain-frequency-time representation with a minimal filtering effort and / or correlation effort.

[0023] A preferred embodiment of the invention creates a digital watermark decoder to provide binary message data, depending on a digital watermark signal. The digital watermark decoder comprises a domain-frequency-time representation provider configured to provide a first domain-frequency-time representation of the digital watermark signal. The digital watermark decoder also comprises a differential decoder configured to derive a second domain-frequency-time representation from the first domain-frequency-time representation, such that the values of the second domain-frequency-time representation depend of phase differences between two corresponding values (and preferably adjacent) of the first domain-frequency-time representation. The digital watermark decoder also comprises a synchronization determiner configured to obtain synchronization information based on the second domain-frequency-time representation. The digital watermark decoder also comprises a digital watermark extractor configured to extract the binary message data of the first time-frequency representation of the digital watermark signal or of the second domain-frequency time representation of the digital watermark signal using synchronization information.

[0024] Another embodiment according to the invention creates a digital watermark decoder to provide binary message data depending on a digital watermark signal. The digital watermark decoder comprises a domain-frequency-time representation provider, configured to provide a first domain-frequency-time representation of the digital watermark signal and a differential decoder. The differential decoder is configured to derive a second domain-frequency-time representation from the first domain-frequency-time representation, such that values of the second domain-frequency-time representation depend on phase differences between two values corresponding to the first domain-frequency-time representation. The digital watermark decoder also comprises a digital watermark extractor configured to extract the binary message data from the second domain-frequency-time representation.

[0025] These modalities according to the invention are based on the finding that the reliability of digital watermark decoding can be improved by evaluating phase differences between adjacent values of a first domain-frequency-time representation, which represents, for example amplitudes or energies and phases of a digital watermarked signal in different frequency bands for a plurality of time intervals. It has been found that differences between adjacent values (for example temporarily adjacent or adjacent in frequency) of the first domain-frequency-time representation, which for example can be derived from the digital watermarked audio signal using a filter bank or using a Fourier transformer or an MDCT transform, they are typically robust with respect to many typical channel distortions, such as sufficiently slow channel changes, or Doppler frequency shifting, and so on. Accordingly, the second domain-frequency-time representation can be obtained in a reliable manner and the second domain-frequency-time representation is therefore insensitive to channel changes, whereby the watermarked signal Digital is transmitted. Accordingly, the digital watermark decoder described above provides a very high degree of reliability.

[0026] In a preferred embodiment, the domain-frequency-time provider is configured to provide, for a plurality of frequency bands and for a plurality of time intervals, soft bit coefficients describing an amplitude and a phase of the digital watermark signal in the respective frequency bands and time intervals. The differential decoder is configured to determine a value of the second domain-frequency-time representation associated with a given frequency band and a given time interval based on two corresponding values of the first domain-frequency-time representation, or a previously version processed from it. Using two values of the first domain-frequency-time representation in order to obtain a value of the second domain-frequency-time representation, it is possible to evaluate the phase differences between the two values of the first domain-frequency-time representation. Processing can be done based on real values and / or complex values. Accordingly, any slow channel changes, which do not have a strongly different impact on adjacent values of the first domain-frequency-time representation, can be approximately offset by using two values of the first domain-frequency-time representation at in order to obtain values from the second domain-frequency-time representation.

[0027] In a preferred embodiment, the digital watermark decoder comprises a filter bank for analysis configured to convolve the digital watermark signal, or its multi-channel to stereo conversion version thereof, with a function of bit formation In this case, the digital watermark decoder is configured to show a convolution result in time, in order to obtain discrete time values of the first domain-frequency-time representation. The digital watermark decoder is configured to adjust a synchronization used for convolving result sampling at a sub-interval-bit resolution depending on a synchronization information, in order to maximize the signal-to-ratio ratio. -Noise and minimize a proportion of symbol interference. It has been found that the output of this analysis filter bank is well suited to serve as the first time-frequency representation for differential decoding. Also, it has been found that differential decoding provides reasonable results for the first domain-frequency-time representation, even if there is a slight misalignment of the synchronization used to sample the result of the convolution.

[0028] In a preferred embodiment, the differential decoder is configured to derive the second domain-frequency-time representation independently for different frequency bands, such that the different phase rotations of the digital watermark signal at different Frequency bands are compensated independently. The synchronization determiner or digital watermark decoder is configured to jointly process a set of values of the second frequency-time representation associated with a given portion of time and different frequency bands, to obtain synchronization information or one bit of the binary message data. It has been found that differential decoding allows reliable joint processing of values of the second domain-frequency-time representation even without using a channel corrector and even without knowledge regarding a channel state. According to this, the inventive concept allows a particularly efficient implementation.

[0029] An embodiment according to the invention creates a device for evaluation of portable digital watermark. The portable digital watermark evaluation device comprises a microphone configured to provide an electric microphone signal and a digital watermark decoder, as discussed above. The digital watermark decoder is configured to receive the microphone signal as the digital watermark signal. It has been found that the digital watermark decoder of the invention can be applied with particular advantage in this portable digital watermark evaluation device, which evaluates an audio signal received by a microphone, because the watermark decoder Digital water is particularly insensitive to typical channel distortions such as Doppler shifts, zero transfer functions and so on.

[0030] Additional modalities according to the invention create a method for providing a digital watermark signal depending on binary message data and a method for providing binary message data depending on a digital watermark signal. Some additional modalities create computer programs to perform the methods. The methods and computer programs are based on the same findings as the apparatus described above.

BRIEF DESCRIPTION OF THE FIGURES

[0031] Modalities according to the invention will be described subsequently with reference to the attached figures, wherein:

Figure 1 shows a schematic block diagram of a digital watermark inserter according to an embodiment of the invention;

Figure 2 shows a schematic block diagram of a digital watermark decoder, according to an embodiment of the invention;

Figure 3 shows a detailed schematic block diagram of a digital watermark generator according to an embodiment of the invention;

Figure 4 shows a detailed block schematic diagram of a modulator, for use in an embodiment of the invention;

Figure 5 shows a detailed block schematic diagram of a psychoacoustic processing module for use in an embodiment of the invention;

Figure 6 shows a schematic block diagram of a psychoacoustic model processor for use in an embodiment of the invention;

Figure 7 shows a graphical representation of an energy spectrum of an audio signal output by block 801 on frequency;

Figure 8 shows a graphical representation of an energy spectrum of an audio signal output by the 802 over frequency block;

Figure 9 shows a schematic block diagram of an amplitude calculation;

Figure 10a shows a schematic block diagram of a modulator;

Figure 10b shows a graphical representation of the location of coefficients in the frequency claim

weather; Figures 11a and 11b show schematic block diagrams of module implementation alternatives of synchronization;

Figure 12a shows a graphic representation of the problem of finding the temporal alignment of a digital watermark;

Figure 12b shows a graphic representation of the problem of identifying the start of the message; Figure 12c shows a graphical representation of a temporal alignment of synchronization sequences in a full message synchronization mode;

Figure 12d shows a graphical representation of the temporal alignment of the synchronization sequences in a partial message synchronization mode; Figure 12e shows a graphical representation of power data of the synchronization module; Figure 12f shows a graphic representation of a concept to identify a synchronization bit; Figure 12g shows a schematic block diagram of a synchronization signature correlator;

Figure 13a shows a graphical representation of an example of temporary concentrate; Figure 13b shows a graphic representation of an example for multiplication as an element between bits and concentrate sequences;

Figure 13c shows a graphical representation of an output of the synchronization signature correlator

after temporary average; Figure 13d shows a graphical representation of the output of a synchronization signature correlator synchronized filtering with the autocorrelation function of the synchronization signature;

Figure 14 shows a schematic block diagram of a digital watermark extractor according to

an embodiment of the invention; Figure 15 shows a schematic representation of a selection of a part of the representation of domain-frequency-time as a candidate message;

Figure 16 shows a schematic block diagram of an analysis module; Figure 17a shows a graphical representation of an output of a synchronization correlator; Figure 17b shows a graphic representation of decoded messages; Figure 17c shows a graphical representation of a synchronization position that is extracted from a signal of

digital watermark;

Figure 18a shows a graphical representation of a payload, a payload with Viterbi termination sequence, a Viterbi encoded payload and a repeat encoded version of the Viterbi encoded payload; Figure 18b shows a graphical representation of subcarriers used to embed a signal mark of

digital water; Figure 19 shows a graphic representation of an uncoded message, of an encoded message, a

synchronization message and a digital watermark signal, where the synchronization sequence is applied to the messages; Figure 20 shows a schematic representation of a first stage of a so-called concept

"ABC synchronization"; Figure 21 shows a graphic representation of a second stage of the concept called “synchronization ABC ”;

Figure 22 shows a graphic representation of a third stage of the so-called "ABC synchronization" concept;

Figure 23 shows a graphic representation of a message comprising a payload and a CRC portion;

Figure 24 shows a schematic block diagram of a digital watermark generator according to an embodiment of the invention;

Figure 25 shows a schematic block diagram of a digital watermark or brand decoder according to an embodiment of the invention;

Figure 26 shows a schematic block diagram of a digital watermark or brand decoder according to an embodiment of the invention; Y

Figure 27 shows a schematic block diagram of a portable digital watermark evaluation device according to an embodiment of the invention;

Figure 28 shows a flow chart of a method for providing a digital watermark signal in dependence on a digital watermark signal; Y

Figure 29 shows a flow chart of a method for providing binary message data in dependence on a digital watermark signal.

Detailed Description of Modalities

1. Generation of digital watermark

1.1 Digital watermark generator according to Figure 24

[0032] Next, a digital watermark generator 2400 will be described with reference to 24, which shows the schematic block diagram of this digital watermark generator. The digital watermark generator is configured to receive binary message data 2410 and to provide a digital watermark signal 2420 based thereon. The digital watermark generator 2400 comprises an information processor 2430, which is configured to provide, depending on the information units (for example, bits) of the binary message data 2410, a first representation of domain-frequency-time 2432 values of which represent the binary message data 2410. The brand generator of digital water 2400 also comprises a differential encoder 2440, which is configured to derive a second domain-frequency-time representation 2442 from the first domain-frequency-time representation 2432, such that the second domain-frequency-time representation 2442 comprises a plurality of values, where a difference between two values of the second domain-frequency-time representation 2442 represents a va corresponding lor of the first domain-frequency-time representation 2432, in order to obtain a differential coding of the values of the first domain-frequency-time representation 2432. The watermark generator 2400 also comprises a signal provider with digital watermark 2450, which is configured to provide the digital watermark signal 2420 based on the second domain-frequency-time representation 2442.

[0033] The 2400 digital watermark generator can be supplemented by any of the features and functionalities discussed in more detail in section 3 below.

1.2 Method for providing a digital watermark signal in dependence on binary message data according to Figure 28

[0034] Next, a method for providing a digital watermark signal depending on the binary message data will be explained with reference to Figure 28, which shows a flow chart of this method. The method 2800 of Figure 28 comprises a step 2810 of providing, depending on the information units of the binary message data, a first domain-frequency-time representation, of which the values represent the binary message data. The method 2800 also comprises a step 2820 of deriving a second domain-frequency-time representation from the first domain-frequency-time representation, such that the second domain-frequency-time representation comprises a plurality of values, wherein a difference between two values of the second domain-frequency-time representation represents a corresponding value of the first domain-frequency-time representation in order to obtain a differential coding of the values of the first domain-frequency-time representation. The method 2800 also comprises a step 2830 of providing the digital watermark signal based on the second domain-frequency-time representation.

[0035] Naturally, method 2800 can be supplemented by any of the features and functionalities discussed herein, also with respect to the apparatus of the invention.

2. Digital watermark decoding

2.1 Digital watermark decoder according to Figure 2

[0036] Next, a digital watermark decoder 2500 will be described with reference to Figure 25, which shows a schematic block diagram of this digital watermark decoder.

[0037] The digital watermark decoder 2500 is configured to provide binary message data 2520, depending on a digital watermark signal 2510. The digital watermark decoder 2500 comprises a domain-frequency representation provider- time 2530, which is configured to provide a first domain-frequency-time representation 2532 of the digital watermark signal 2510. The digital watermark decoder 2500 also comprises a differential decoder 2540, which is configured to derive a second representation of domain-frequency-time 2542 from the first representation of domain-frequency-time 2532, such that the values of the second representation of domain-frequency-time 2542 depend on phase differences between two corresponding values (and preferably adjacent) of the first domain-frequency-time representation 2532.

[0038] Naturally, the digital watermark decoder 2500 may be supplemented by any of the features and functionalities discussed herein with respect to digital watermark decoding.

2.2 Digital watermark decoder according to Figure 26

[0039] Next, a digital watermark decoder 2600 will be described with reference to Figure 26, which shows a schematic block diagram of this digital watermark decoder. The digital watermark decoder 2600 is configured to receive a digital watermark signal 2610 and, based on this, provide binary message data 2620. The digital watermark decoder 2600 comprises a domain-frequency representation provider. -time 2630 configured to provide a first domain-frequency-time representation 2632 of the watermark signal 2610. The digital watermark decoder 2600 also comprises a differential decoder 2640 configured to derive a second domain-frequency representation- time 2642 of the first domain-frequency representation time 2632, such that the values of the second domain-frequency-time representation depend on phase differences between two corresponding values (and preferably temporarily adjacent or adjacent in frequency) of the first representation domain-frequency-time 2632. The watermark decoder dig ital 2600 also comprises a digital watermark extractor 2650, which is configured to extract binary message data 2620 from the second domain-frequency-time representation 2642.

[0040] Naturally, the digital watermark decoder 2600 can be supplemented by any of the means and functionalities discussed herein with respect to digital watermark decoding.

2.3. Digital watermark evaluation device in accordance with Figure 27

[0041] Next, a portable digital watermark evaluation device will be described, referring to Figure 27, which shows a schematic block diagram of this device 2700.

[0042] The portable digital watermark evaluation device 2700 comprises a microphone 2710 configured to provide an electrical microphone signal 2712. The portable digital watermark evaluation device 2700 also comprises a digital watermark decoder 2720, which may be identical to the digital watermark decoders described herein. The digital watermark decoder 2720 is configured to receive the microphone signal 2712 as a digital watermark signal to provide binary message data 2722 based on it.

[0043] Naturally, the 2720 digital watermark decoder can be supplemented by any of the means and functionalities described herein with respect to the digital watermark decoder.

2.4. Method for providing binary message data depending on a digital watermark signal according to Figure 29

[0044] Next, a method 2900 for providing binary message data in dependence on a digital watermark signal will be described with reference to Figure 29, which shows a flow chart of this method.

[0045] Method 2900 comprises a step 2910 of providing a first time-frequency representation of the digital watermark signal. The method 2900 also comprises a step 2920 of deriving a second domain-frequency-time representation from the first domain-frequency-time representation, such that the values of the second domain-frequency-time representation depend on phase differences between two values. corresponding (and preferably adjacent) of the first domain-frequency-time representation.

[0046] Method 2900 also comprises a step 2930 of using the second time-frequency-time representation to determine a synchronization information, which is used to provide the binary message data or extract the binary message data from the signal marked with digital water

[0047] Method 2900 can be supplemented by any of the features and functionalities described herein with respect to digital watermark decoding.

3. System Description

[0048] Next, a system for digital watermark transmission will be described, comprising a digital watermark inserter and a digital watermark decoder. Naturally, the digital watermark inserter and the digital watermark decoder can be used independently of each other.

[0049] For the description of the system, a hierarchical approach to the system here is chosen. First, it distinguishes between encoder and decoder. Then, in sections 3.1 to 3.5 each processing block is described in detail.

[0050] The basic structure of the system can be seen in Figures 1 and 2, which illustrate the encoder and decoder side, respectively. Figure 1 shows a schematic block diagram of a digital watermark inserter 100. On the coding side, the digital watermark signal 101b is generated in the processing block 101 (also designated as a digital watermark generator ) from binary data 101a and based on information 104, 105 exchanges with the psychoacoustic processing module 102. The information provided from block 102 typically ensures that the digital watermark is inaudible. The digital watermark produced by the digital watermark generator 101 is then added to the audio signal 106. The digital watermark signal 107 can then be transmitted, stored or further processed. In the case of a multimedia file, for example an audio-video file, it is necessary to add an appropriate delay to the video stream so as not to lose the audio-video synchrony. In the case of a multi-channel audio signal, each channel is processed separately as explained in this document. Processing blocks 101 (digital watermark generator) and 102 (psychoacoustic processing module) are explained in detail in Sections 3.1 and 3.2, respectively.

[0051] The decoder side is illustrated in Figure 2, which shows a schematic block diagram of a digital watermark detector 200. An audio signal with digital watermark 200a, for example recorded by a microphone, is made available to the system 200. A first block 203, which is also designated as an analysis module, demodulates and transforms the data (for example, the digital watermarked audio signal) into a time / frequency domain (thus obtaining a representation of domain-frequency-time 204 of the audio signal with digital watermark 200a) passes it to the synchronization module 201, which analyzes the power signal 204 and transports a temporary synchronization, that is, determines the temporal alignment of the coded data (for example of coded digital watermark data regarding the frequency-time domain representation). This information (for example, the resulting synchronization information 205) is given to the digital watermark extractor 202, which decodes the data (and consequently provides the binary data 202a, which represents the data content of the branded audio signal of digital water 200a).

3.1 The digital watermark generator 101

[0052] The digital watermark generator 101 is illustrated in detail in Figure 3. Binary data (expressed as ± 1) to hide the audio signal 106 is given to the digital watermark generator 101. Block 301 organizes 101a data in a package of equal length Mp. Supplementary bits (for example, added) are added for signaling purposes to each packet. Let it be that you give it its number. Its use will be explained in detail in Section 3.5. It should be noted that below each packet of payload bits together with the additional signaling bits is denoted message.

[0053] Each message 301a of length Nm = Ms + Mp is transferred to the processing block 302, the channel encoder, which is responsible for encoding the bits for error protection. One possible modality of this module consists of a convolutional encoder together with an interleaver. The proportion of the convolutional encoder greatly influences the total degree of protection against errors of the digital watermark system. The interleaver, on the other hand, is protected against bursts of interference or noise. The interleaver's operating range may be limited to one message, but it may also extend to more messages. Let Rc denote the proportion of code, for example 1/4. The number of bits encoded by each message is Nm / Rc. The channel encoder provides, for example, a binary message encoded 302a.

[0054] The next processing block, 303 transports a spread or spread in frequency domain. In order to achieve sufficient signal to interference ratio, the information (for example, the information in binary message 302a) is propagated and transmitted in Nf carefully selected subbands. Its exact position in frequency is decided a priori and is known for both the encoder and the decoder. Details on the selection of this important system parameter are given in Section 3.2.2. The frequency propagation is determined by the propagation sequence Cf with size Nf X1. Output 303 of block 303 consists of Nf Bit currents, one for each sub-band. The ith bit stream is obtained by multiplying the feed bit with the ith component of the propagation sequence Cf. The simplest propagation consists of copying the bit stream to each output stream, that is, use of a Spread sequence of all ones.

[0055] Block 304, which is also designated as a synchronization scheme inserter, adds a synchronization signal to the bit stream. A robust synchronization is important since the decoder does not know the temporal alignment of bits or the data structure, that is, when each message begins. The synchronization signal consists of Ns sequences of Nf bits each. Sequences are elements multiplied and periodically to the bit stream (or Bit streams 303a). For example, let a, b, and c be the Ns = 3 synchronization sequences (also designated as synchronization propagation sequences). Block 304 multiplies a to the first propagation bit, b to the second propagation bit and c to the third propagation bit. For the following bits, the process is periodically iterated, that is a to the fourth bit, b for the fifth bit and so on. Accordingly, a combined synchronization-information information 304a is obtained. Synchronization sequences (also referred to as synchronization propagation sequences) are carefully chosen to minimize the risk of false synchronization. More details are given in the Section

3.4. Also, it should be noted that a sequence a, b, c, ... can be considered as a sequence of synchronization propagation sequences.

[0056] Block 305 carries a time domain propagation. Each propagation bit at the input, ie a vector of length Nf, is repeated in time domain Nt times. Similar to frequency propagation, we define a ct propagation sequence with size Ntx1. The i-th temporal repetition is multiplied with the i-th component of ct.

[0057] The operations of blocks 302 to 305 can be put in mathematical terms as follows. Let m of size 1 be an encoder message, output 302. Output 303a (which can be considered as a representation of propagation information R) of block 303 is

cfm with size Nf x Nm / Rc

       (one)

output 304a of block 304, which can be considered as a combined representation of synchronization information C, is

S ° (cfm) of size Nf x Nm / Rc

       (2)

where ° denotes the product by Schur elements - and

S = [. . . a b c. . . a b. . . ] size Nf x Nm / Rc

       (3)

[0058] Exit 305a of 305 is

(S ° (cfm)) or cTt of size Nf x Nt · Nm / Rc

       (4)

where ° and T denote the product Kronecker and transposition, respectively. Please remember that binary data are expressed as ± 1.

[0059] Block 306 performs differential bit coding. This stage gives the system additional robustness against phase shifts due to local oscillator movement or mismatches. More details on this matter are given in Section 3.3. If b (i; j) is the bit for the ith frequency band and the jth time block at the input of block 306, the output bit bdiff (i; j) is

bdiff (i, j) = bdiff i, j - 1) · b (i, j).

       (5) [0060] At the beginning of the current, this is for j = 0, bdiff (i, j - 1) is set to 1.

[0061] Block 307 conveys the current modulation, that is, the generation of the waveform of the signal from

5 digital watermark depending on the binary information 306a given in your feed. A more detailed schematic is given in Figure 4. Nf parallel feeds, 401 to 40Nf contain the bit currents for the different subbands. Each bit of each sub-band current is processed by a bit forming block (411 to 41Nf). The output of the bit shaping blocks are time domain waveforms. The waveform generated for the jth time block and the ith sub-band denoted by Si, j (t), based on the feed bit

10 bdiff (i, j) is calculated as follows

       (6) where y (i, j) is a weighting factor that is provided by the psychoacoustic processing unit 102,

Tb is the bit time interval, and gi (t) is the bit formation function for the ith sub-band. The bit formation function is obtained from a base frequency function giT (t) frequency modulated with a cosine

       (7) where fi is the center frequency of the ith sub-band and the superscript T represents the transmitter. The

20 baseband functions may be different for each subband. If identical are chosen, a more efficient implementation in the decoder is possible. See Section 3.3 for more details.

[0062] Bit shaping for each bit is repeated in an iterative process controlled by the psychoacoustic processing module (102). Iterations are necessary for fine adjustment of weights and (i, j) to allocate as much energy as possible to the digital watermark while remaining inaudible. More details are given in Section 3.2.

[0063] The complete waveform at the output of the i-th 4li bit shaping filter is

          (8)

[0064] The bit that forms the baseband function giT (t) is usually not zero for a time interval much larger than Tb, although the main energy is concentrated within the bit range. An example can be seen in Figure 12a, where the same bit that forms the baseband function is traced to two adjacent bits. In the figure we have Tb = 40 ms. The selection of Tb as well as the form of the function considerably affects the system.

35 In fact, longer symbols provide narrower frequency responses. This is particularly beneficial in reverberant environments. In fact, in these scenarios, the digital watermark signal reaches the microphone through several propagation routes, each characterized by a different propagation time. The resulting channel exhibits strong frequency selectivity. Interpreted in time domain, longer symbols are beneficial as echoes with a delay comparable to the constructive interference that yields the bit interval, which

40 means that they increase the received signal energy. However, longer symbols can also lead to some disadvantage accounts; Larger overlays can lead to inter-symbol interference (IS I) and are surely more difficult to hide in the audio signal, so that the psychoacoustic processing module will allow less energy than for shorter symbols.

3.2 The Psychoacoustic Processing Module 102

[0066] As illustrated in Figure 5, the psychoacoustic processing module 102 consists of 3 parts. The first stage is an analysis module 501 that transforms the audio signal in time into a time / frequency domain. This analysis module can carry parallel analyzes in different time / frequency resolutions. After the analysis module, the time / frequency data is transferred to the psychoacoustic model (PAM) 502, where masking thresholds for the digital watermark signal are calculated according to psychoacoustic considerations (see E. Zwicker H. Fastl , "Psychoacoustics Facts and models"). The masking thresholds indicate the amount of energy that can be hidden in the audio signal for each subband and time block. The last block in the psychoacoustic processing module 102 illustrates the amplitude calculation module 503. This module determines the amplitude gains to be used in the generation of the digital watermark signal, such that masking thresholds are satisfied. , that is to say the embedded energy is less than or equal to the energy defined by the masking thresholds.

3.2.1 The 501 Time / Frequency Analysis

[0067] Block 501 transports the time / frequency transformation of the audio signal by an overlapping transform. The best audio quality can be achieved when multiple time / frequency resolutions are made. An efficient modality of an overlapping transform is the short-time Fourier transform (STFT = short-time Fourier transform), which is based on fast Fourier transforms (FFT = fast Fourier transforms) of window time locks. The length of the window determines the resolution of time / frequency, so that longer windows produce resolutions of shorter time and higher frequency, while shorter windows vice versa. The shape of the window, on the other hand, among other things, determines the frequency leak.

[0068] For the proposed system, we achieved an inaudible watermark by analyzing the data with two different resolutions. A first bank of filters is characterized by a jump size of Tb, ie the bit length. The jump size is the time interval between two adjacent time blocks. The window length is approximately Tb. Please note that the shape of the window does not have to be the same as that used for bit shaping, and in general you should model the human auditory system. Numerous publications study this problem.

[0069] The second filter bank applies a shorter window. The superior temporal resolution achieved is particularly important when a digital watermark is embedded in speech, since its temporal structure is generally thinner than Tb.

[0070] The sampling rate of the feed audio signal is not important, as long as it is large enough to describe the watermark signal without overlapping. For example, if the largest frequency component contained in the digital watermark signal is 6 kHz, then the sampling rate of the time signals must be at least 12 kHz.

3.2.2 The 502 Psychoacoustic Model

[0071] The psychoacoustic model 502 has the task of determining the masking thresholds, that is, the amount of energy that can be hidden in the audio signal by each sub-band and blocks the time keeping the water signal with watermark digital indistinguishable from the original.

(min) and fi (max)

[0072] The i-th sub-band is defined between two limits, ie fi. Subbands are determined at

(max) = fi

define Nf center frequencies fi and where fi-1 (min) i is for i = 2, 3, ..., Nf. An appropriate selection for the center frequencies is given by the Bark scale proposed by Zwicker in 1961. The subbands become larger for higher center frequencies. A possible implementation of the system uses 9 subbands in the 1.5 to 6 kHz range arranged in an appropriate manner.

[0073] The following processing steps are carried out separately for each time / frequency resolution for each sub-band and each time block. Processing step 801 performs a spectral smoothing. In fact, tonal elements, as well as notches in the energy spectrum, need to be smoothed. This can be done in several ways. A hue measure can be calculated and then used to direct an adaptive smoothing filter. Alternatively, in a simpler implementation of this block, a medium type filter can be used. The median filter considers a vector of values and sends out its median value. In a medium type filter, the value corresponding to a different quantile than 50% can be selected. The filter width is defined in Hz and is applied as a nonlinear moving average that starts at the lowest frequencies and ends at the highest possible frequency. The 801 operation is illustrated in Figure 7. The red curve is the smoothing output.

[0074] Once the smoothing has been carried out, the thresholds are calculated by block 802 considering only frequency masking. Also, in this case there are different possibilities. One way is to use the minimum for each sub-band to calculate the masking energy Ei. This is the equivalent energy of the signal that effectively operates as a masking. From this value, we can simply multiply a certain scale adjustment factor to obtain the masked energy Ji. These factors are different for each subband and time / frequency resolution and are obtained by empirical psychoacoustic experiments. These stages are illustrated in Figure 8.

[0075] In block 805, it is considered temporary masking. In this case, different blocks of time for the same sub-band are analyzed. The masked energies Ji are modified according to an after-masking profile derived empirically. Consider two adjacent blocks of time, that is, k-1 and k. The corresponding masking energies are Ji (k-l) and Jj (k). The post-masking profile defines that, for example, the masking energy Ex can mask an energy Ji at time k and a · Ji at time k + 1. In this case, block 805 compares Jj (k) (the energy masked by the current time block) and a · Ji (k + 1) (the energy masked by the previous time block) and selects the maximum. Post-masked profiles are available in the literature and have been obtained by empirical psychoacoustic experiments. It should be noted that for a large Tb, that is> 20 ms, post-masking is applied only to the time / frequency resolution with shorter time windows.

[0076] In summary, at the exit of block 805 we have the masking thresholds for each sub-band and time block that are obtained for two different time / frequency resolutions. The thresholds have been obtained by considering both phenomena of masked time and frequency. In block 806, the thresholds for the different time / frequency resolutions are merged. For example, one possible implementation is that 806 considers all the thresholds corresponding to the time and frequency intervals where a bit is assigned, and selects the minimum.

3.2.3 The 503 Amplitude Calculation Block

[0077] Please refer to Figure 9. The 503 feed is the 505 thresholds of the 502 psychoacoustic model where all psychoacoustic motivated calculations are carried out. In the 503 amplitude calculator, additional calculations are made with the thresholds. First, an amplitude mapping 901 is carried out. This block only converts the masking thresholds (normally expressed as energy) into amplitudes that can be used to scale the bit shaping function defined in Section 3.1. Subsequently, the amplitude adaptation block 902 is executed. This block iteratively adapts the amplitudes and (i, j) that are used to multiply the bit shaping functions in the digital watermark generator 101, such that the masking thresholds are certainly filled. In fact, as already discussed, the bit shaping function normally extends over a time interval greater than Tb. Therefore, multiply the correct amplitude and (i, j) that meets the masking threshold at point i, j does not necessarily meet the requirements at point i, j-1. This is particularly crucial in strong beginnings, as a pre-echo becomes audible. Another situation that needs to be avoided is the unfortunate overlap in the tails of different bits that can lead to an audible digital watermark. Therefore, block 902 analyzes the signal generated by the digital watermark generator to verify if the thresholds have been met. If not, modify the amplitudes and (i, j) in accordance.

[0078] This concludes the encoder side. The following sections deal with the processing steps that are carried out in the receiver (also designated as a digital water decoder).

3.3 The Analysis Module 203

[0079] The analysis module 203 is the first stage (or block) of the digital watermark extraction process. Its purpose is to transform the audio signal with digital watermark 200a back to Nf bit streams

 (also designated 204), one for each spectral sub-band i. These are further processed by the synchronization module 201 and the digital watermark extractor 202, as discussed in Sections 3.4 and

3.5, respectively. It should be noted that

they are soft bit streams, that is, they can take, for example, any real value and without having made a hard decision on the bit.

[0080] The analysis module consists of three parts that are illustrated in Figure 16: The analysis filter bank 1600, the amplitude normalization block 1604 and the differential decoding 1608.

3.3.1 Analysis filter bank 1600

[0081] The digital watermark audio signal is transformed into the time-frequency domain by the analysis filter bank 1600 shown in detail in Figure 10a. The filter bank power is the audio signal with digital watermark received r (t). Its output is the complex coefficients biAFB (j) for the ith branch or sub-band at the instant of time j. These values contain information regarding the amplitude and phase of the signal at the center frequency fi and the time j · Tb.

[0082] The filter bank 1600 consists of Nf branches, one for each spectral sub-band i. Each branch is divided into an upper sub-branch for the phase component and a lower sub-branch for the quadrature component of sub-band i. Although the modulation in the digital watermark generator and in this way the digital watermark audio signal are purely real evaluation, the analysis of

The complex value of the signal in the receiver is required because rotations of the modulation constellation introduced by the channel and synchronization misalignments are not known in the receiver. Next we consider the ith branch of the filter bank. By combining the sub-branching in phase and quadrature, we can define the baseband signal of complex value b iAFB (j) as

10 where * indicates convolution and giR (t) is the impulse response of the sub-band receiver low pass filter i. Usually giR (t) i (t) is equal to the base band bit formation function giT (t) of sub-band i in modulator 307 in order to meet the coupled filter condition, but they are also possible Other impulse responses.

[0083] In order to obtain the biAFB coefficients (j) with the velocity of l = Tb, the continuous output biAFB (j) must be

15 sampled. If the correct bit synchronization is known by the receiver, sampling with speed 1 = Tb will be sufficient. However, since bit synchronization is not yet known, sampling is carried out with the Nos / Tb rate where Nos is the oversampled factor of analysis filter bank. By selecting Nos large enough (e.g. Nos = 4), we can ensure that at least one sampling cycle is close enough to the ideal bit synchronization. The decision in the best oversampled layer is made

20 during the synchronization process, so that all oversampled data is maintained until then. This process is described in detail in Section 3.4.

[0084] At the output of the ith branch we have the biAFB coefficients (j, k) where j indicates the bit number or the instant of time and k indicates the oversampled position within this single bit, where k = one ; 2; ...., Nos.

[0085] Figure 10b gives an exemplary overview of the location of the coefficients in the time plane. The oversampled factor is Nos = 2. The height and width of the rectangles respectively indicates the bandwidth and time interval of the part of the signal that is represented by the corresponding coefficient biAFB (j, k).

[0086] If the subband frequencies fi are chosen as multiples of a certain Lf interval, the analysis filter bank can be efficiently implemented with the Fast Fourier Transform (FFT = Fast Fourier Transform).

3.3.2 Standardization of Amplitude 1604

[0087] Without loss of generality and to simplify the description, we consider that bit synchronization is known and that Nos = 1 below. That is, we have complex biAFB coefficients (j) at the power supply of the standardization block 1604. Since no channel status information is available at the receiver (i.e. the propagation channel is unknown), a combination scheme is used equal gain (EGC = equal gain

40 combining). Due to the time and frequency dispersion channel, the energy of the bit sent bi (j) is not only around the central frequency fi and the time instant j, but also at adjacent frequencies and instants of time. Therefore, for a more precise weighting, additional coefficients are calculated at the frequencies fj ± n Lf and used for normalization of the biAFB coefficient (j). If n = 1 we have, for example,

[0088] Normalization for n> 1 is a direct extension of the above formula. In the same way we can also choose to normalize soft bits when considering more than an instant of time. Normalization is carried out for each sub-band i and every moment of time j. The current combination of EGC is carried out in later stages of the extraction process.

50 3.3.3 Differential decoding 1608

[0001] In the supply of the differential decoding block 1608 we have complex coefficients normalized in binorm amplitude (j) that contains information regarding the phase of the signal components at the

fi frequency and time instant j. Since the bits are differentially encoded in the transmitter, the reverse operation must be performed here. Soft bits are obtained by first calculating the phase difference of two

[0090] This must be carried out separately by each sub-band because the channel normally introduces different phase rotations in each sub-band.

3.4 The Synchronization Module 201

10 [0091] The task of the synchronization module is to find the temporal alignment of the digital watermark. The problem of synchronizing the decoder to the encoded data is twofold. In a first stage, the analysis filter bank must be aligned with the encoded data, that is, the giT (t) bit shaping functions used in the synthesis in the modulator must be aligned with the giR (t) filters used for the analysis. This

The problem is illustrated in Figure 12a, where the analysis filters are identical to those of synthesis. At the top, three bits are visible. For simplicity, the waveforms for all three bits have not been scaled. The temporal offset between different bits is Td. The lower part illustrates the synchronization aspect in the decoder: the filter can be applied at different times in time, however, only the position marked in red (curve 1299a) is correct and allows the first bit to be extracted with the best signal ratio to noise

20 (SNR = signal to noise ratio) and signal to interference ratio (SIR = signal to interference ratio). In fact, an incorrect alignment will lead to degradation of both SNR and SIR. We refer to this first alignment aspect as "bit synchronization." Once bit synchronization has been achieved, bits can be optimally extracted. However, to correctly decode a message, it is necessary to know at what bit a new message begins. This aspect is illustrated in Figure 12b and referred to as message synchronization. In the

25 decoded bit stream only the initial position marked in red (position 1299b) is correct and allows the k-th message to be decoded.

[0092] First we only attend the synchronization message. The synchronization signature, as explained in Section 3.1, is composed of Ns sequences in a predetermined order that are embedded continuously and

30 periodic in the digital watermark. The synchronization module is capable of recovering the temporal alignment of the synchronization sequences. Depending on the size Ns we can distinguish between two modes of operation, which are illustrated in Figures 12c and 12d, respectively.

[0093] In the full message synchronization mode (Figure 12c) we have Ns = Nm / Rc. For simplicity in

We consider Ns = Nm / Rc = 6 and without time propagation, that is, Nt = 1. The synchronization signature used, for purposes of illustration, is shown below the messages. Actually, they are modulated depending on the code bits and frequency propagation sequences, as explained in Section 3.1. In this mode, the periodicity of the synchronization signature is identical to that of the messages. The synchronization module can therefore identify the start of each message by finding the temporal alignment of the

40 sync signature. We refer to the temporary positions in which a new synchronization signature begins as synchronization successes. The synchronization hits are then passed to the digital watermark extractor 202.

[0094] The second possible mode, the partial message synchronization mode (Figure 12d), is illustrated in Figure

45 12d. In this case we have Ns <Nm = Rc. In the figure we have taken Ns = 3, so that the three synchronization sequences are repeated twice for each message. Please note that the periodicity of the messages does not have to be multiplied by the periodicity of the synchronization signature. In this mode of operation, not all synchronization hits correspond to the start of a message. The synchronization module has no means to distinguish between successes and this task is given to the digital watermark extractor 202.

[0095] The processing blocks of the synchronization module are illustrated in Figures 11a and 11b. The synchronization module performs bit synchronization and message synchronization (either full or partial) immediately upon analyzing the output of the synchronization signature correlator 1201. The data in the time / frequency domain 204 is provided by The analysis module. Since bit synchronization is not yet available, block 203 oversamples the data with the Nos factor, as described in Section 3.3. An illustration of the feeding data is given in Figure 12e. For this example we have taken Nos = 4, Nt = 2, and Ns = 3. In other words, the synchronization signature consists of 3 sequences (denoted with a, b, and c). Time propagation, in this case with propagation sequence ct = [1 1] T, simply repeats each bit twice in the time domain. The exact synchronization hits are denoted with arrows and correspond to the start of each synchronization signature. The synchronization signature period is Nt · Nos · Ns = NSbl, which is 2 · 4 · 3 = 24, for example. Due to the periodicity of the synchronization signature, the synchronization signature correlator (1201) arbitrarily divides the time axis into blocks, called search blocks, with size Nsbl, whose subscript represents the search block length. Each search block must contain (or typically contain) a synchronization success as illustrated in Figure 12f. Each of the Nsbl bits is a successful candidate sync. The task of block 1201's is to calculate a probability measure for each candidate bit of each block. This information is then passed to block 1204 that calculates the synchronization hits.

3.4.1 The synchronization signature correlator 1201

[0096] For each of the candidate synchronization positions Nsbl the synchronization signature correlator calculates a probability measure, the latter is larger and more likely is that the temporal alignment (both bit and partial or full message synchronization) be found. The processing steps are illustrated in Figure 12g.

[0097] Accordingly, a sequence 1201a of probability values, associated with different position selections, can be obtained.

[0098] Block 1301 carries out the temporal concentration, that is, multiplies each Nt bits with the temporal propagation sequence ct and then adds them. This is carried out by each of the frequency subbands Nf. Figure 13a shows an example. We take the same parameters as described in the previous section, that is, Nos = 4, Nt = 2, and Ns = 3. The candidate synchronization position is marked. From that bit, with Nos deactivated, Nt · Ns are taken with block 1301 and concentrated in time with Ct sequences, so that the Ns bits remain.

[0099] In block 1302 the bits are multiplied by elements with the propagation sequences Ns (see Figure 13b).

[0100] In block 1303 the frequency concentration is carried out, that is, each bit is multiplied with the propagation sequence Cf and then summed over the frequency.

[0101] At this point, if the synchronization position was correct, we would have Ns decoded bits. Since the bits are not known to the receiver, block 1304 calculates the probability measure by taking the absolute values of the Ns and sum values.

[0102] The output of block 1304 is in principle a non-coherent correlator that searches for the synchronization signature. In fact, when a small Ns is chosen, that is, the partial message synchronization mode, it is possible to use synchronization sequences (for example a, b, c) that are mutually orthogonal. In doing so, when the correlator does not align correctly with the signature, its output will be very small, ideally zero. When using the full message synchronization mode, it is recommended to use the most possible orthogonal synchronization sequences, and then create a signature to carefully choose the order in which they are used. In this case, the same theory can be applied when propagation sequences with good auto correlation functions are sought. When the correlator is only slightly misaligned, then the correlator output will not be zero even in the ideal case, but it will be smaller in any case compared to the perfect alignment, since the analysis filters cannot optimally capture the energy signal

3.4.2 Calculation of synchronization hits 1204

[0103] This block analyzes the output of the synchronization signature correlator to decide where the synchronization positions are. Since the system is substantially robust against misalignments of up to Tb / 4 and the Tb is usually taken around 40 ms, it is possible to integrate the 1201 output over time to achieve a more stable synchronization. A possible implementation of this is given by an IIR filter applied over time with an impulse response with exponential degradation. Alternatively, an average filter with traditional FIR movement can be applied. Once the averaging has been carried out, a second correlation on different Nt · Ns is carried out ("different position selection"). In fact, we want to exploit the information that the auto-correlation function of the synchronization function is known. This corresponds to a maximum probability estimator. The idea is shown in Figure 13c. The curve shows the output of block 1201 after temporary integration. A possibility to determine the synchronization success has simply found the maximum of this function. In Figure 13d we see the same function (in black) filtered with the auto correlation function of the synchronization signature. The resulting function is plotted in red. In this case the maximum is more pronounced and gives us the position of the synchronization success. The two methods are substantially similar for high SNR but the second method is performed and performs much better with lower SNR regimens. Once the synchronization hits have been found, they are passed to the digital watermark extractor 202 that decodes the data.

[0104] In some modes, in order to obtain a robust synchronization signal, synchronization is performed in the partial message synchronization mode with short synchronization signatures. For this reason, many decodes must be performed, increasing the risk of false positive message detections. To avoid this, in some modalities signaling sequences can be inserted in messages with a lower bit rate as a consequence.

[0105] This approach is a solution to the problem that arises from a synchronization signature shorter than the message, which was already addressed in the previous description of enhanced synchronization. In this case, the decoder does not know when a new message starts and tries to decode to several synchronization points. To distinguish between legitimate and false positive messages, in some modalities a signaling word is used (ie the payload is sacrificed to embed a known control sequence). In some modalities, a plausibility check (alternately or additionally) is used to distinguish between legitimate and false positive messages.

3.5 The digital watermark extractor 202

[0106] The parts constituting the digital watermark extractor 202 are illustrated in Figure 14. This has two inputs, that is 204 and 205 of blocks 203 and 201, respectively. Synchronization module 201 (see Section 3.4) provides synchronization date stamps, that is, the time domain positions at which a candidate message begins. More details of this matter are given in Section 3.4. The filter bank block for analysis 203, on the other hand, provides the data in the time / frequency domain ready to be decoded.

[0107] The first processing stage, the data selection block 1501, selects from the feed 204 the part identified as a candidate message for decoding. Figure 15 shows this procedure in graphic form. Feed 204 consists of Nf real value currents. Since the time alignment is not known to the decoder a priori, the analysis block 203 performs a frequency analysis with a speed greater than 1 / Tb Hz (over sampled). In Figure 15 we must use a sampled envelope factor of 4, that is, 4 vectors with size Nf x 1 are sent out every Tb seconds. When the synchronization block 201 identifies a candidate message, it sends a date stamp 205 indicating the starting point of a candidate message. Selection block 1501 chooses the information required for decoding, that is an array with size Nf xNm / Rc. This matrix 1501a is given to block 1502 for further processing.

[0108] Blocks 1502, 1503, and 1504 perform the same operations as blocks 1301, 1302, and 1303 explained in Section 3.4.

[0109] An alternate embodiment of the invention consists in avoiding the calculations made in 1502-1504 by allowing the synchronization module to also supply the data to be decoded. Conceptually it is a detail. From the point of view of implementation, it is only a matter of how the dampers are made. However, doing the calculations again allows us to have smaller buffers.

[0110] Channel decoder 1505 performs the inverse operation of block 302. If the channel encoder, in a possible mode of this module, consists of a convolutional encoder together with an interleaver, then the channel decoder will perform the deinterleaving. and convolutional decoding, for example, with the well-known Viterbi algorithm. At the exit of this block we have Nm bits, that is, a candidate message.

[0111] Block 1506, the signaling and plausibility block, decides whether the incoming candidate message is really a message or not. For this, different strategies are possible.

[0112] The basic idea is to use a signaling word (such as a CRC sequence) to distinguish between true and false messages. This however reduces the number of available bits as payload. Alternatively, we can use plausibility checks. If the messages for example contain a date stamp, consecutive messages must have consecutive date stamps. If a decoded message has a date stamp that is not of the correct order, we can discard it.

[0113] When a message has been correctly detected, the system can choose to apply the preview and / or backward view mechanisms. We believe that both message and bit synchronization have been achieved. Considering that the user is not jumping (zapping), the system "looks back" in time and tries to decode past messages (if they are not already decoded) using the same synchronization point (backward view approach). This is particularly useful when the system starts. Even more, in bad conditions, it can take two messages to achieve synchronization. In this case, the first message has no possibility. With the view back option, we can save "good" messages that have not been received only due to backward synchronization. The preview is the same but it works towards the future. If we have a message now we know where the next message should be, and we can try to decode it in any way.

3.6. Synchronization Details

[0114] For coding a payload, for example a Viterbi algorithm can be used. Figure 18a shows a graphic representation of a payload 1810, a termination sequence Viterbi 1820, a payload encoded Viterbi 1830 and a repeat code version 1840 of a payload encoded Viterbi. For example, the payload length may be 34 bits and the Viterbi termination sequence may comprise 6 bits. If, for example, a Viterbi code rate of 1/7 can be used, the Viterbi encoded payload can comprise (34 + 6) * 7 = 280 bits. In addition, by using a repeat coding of 1/2, the coded repeat version 1840 of the Viterbi 1830 encoded payload may comprise 280 * 2 = 560 bits. In this example, consider a bit time interval of 42.66 ms, the message length will be 23.9 s. The signal can be embedded for example with 9 subcarriers (for example placed in accordance with the critical bands) of 1.5 to 6 kHz as indicated by the frequency spectrum shown in Figure 18b. Alternatively, also another number of subcarriers (for example 4, 6, 12, 15 or a number between 2 and 20) within a frequency range between 0 and 20 kHz can be used.

[0115] Figure 19 shows a schematic illustration of the basic concept 1900 for synchronization, also called ABC sync. It shows a schematic illustration of an uncoded message 1910, a coded message 1920 and a synchronization sequence (sync sequence) 1930 as well as the application of the sync to several messages 1920 one after another.

[0116] The synchronization sequence or sync sequence mentioned in connection with the explanation of this synchronization concept (shown in Figures 19-23) may be the same as the synchronization signature mentioned above.

[0117] In addition, Figure 20 shows a schematic illustration of the synchronization found when correlated with the sync sequence. If the synchronization sequence 1930 is shorter than the message, more than one synchronization point 1940 (or alignment time block) can be found within a single message. In the example shown in Figure 20, 4 synchronization points are found within each message. Therefore, for each synchronization found, a Viterbi decoder (a Viterbi decoding sequence) can be started. Thus, for each synchronization point 1940 a message 2110 can be obtained, as indicated in Figure 21.

[0118] Based on these messages, true messages 2210 can be identified by a CRC sequence (cyclic redundancy check sequence) and / or plausibility check, as shown in Figure 22.

[0119] CRC detection (cyclic redundancy verification detection) can use a known sequence to identify true false positive messages. Figure 23 shows an example for a CRC sequence added at the end of a payload.

[0120] The probability of false positive (a message generated based on an erroneous synchronization point) may depend on the length of the CRC sequence and the number of Viterbi decoders (number of synchronization points within a single message) initiated. To increase the length of the payload without increasing the probability of false positive, a plausibility (plausibility test) can be exploited or the length of the synchronization sequence (synchronization signature) can be increased.

4. Concepts and Advantages

[0121] Next, some aspects of the system discussed above, which are considered innovative, will be described. Also, the relationship of these aspects to state-of-the-art technologies will be discussed.

4.1. Continuous synchronization

[0122] Some modes allow continuous synchronization. The synchronization signal, which we denote a synchronization signature, is embedded continuously and parallel to the multiplication data with sequences (also designated as synchronization propagation sequences) known to both the transmitting and receiving side.

[0123] Some conventional systems use special symbols (different from those used for the data), while some modalities according to the invention do not use these special symbols. Other classical methods consist of embedding a known sequence of bits (preamble) multiplexed in time with the data, or embedding a signal multiplexed in frequency with the data.

[0124] However, it has been found that using dedicated subbands for synchronization is undesirable, since the channel may have notches on those frequencies making synchronization unreliable. Compared to the other methods, where a preamble or a special symbol is multiplexed in time with the data, the method described here is more advantageous as the method described here allows tracking changes in synchronization (due for example to movement) continually.

[0125] In addition, the energy of the digital watermark signal is unchanged (for example by the multiplicative introduction of the digital watermark in the representation of propagation information) and the synchronization can be designed independent of the psychoacoustic model and speed of data. The length in time of the synchronization signature, which determines the robustness of the synchronization, can be designed at will completely independent of the data rate.

[0126] Another classic method is to embed a synchronization sequence code multiplexed with the data. When compared to this classic method, the advantage of the method described here is that the energy of the data does not represent an interference factor in the calculation of the correlation, providing more robustness. In addition, when code multiplexing is used, the number of orthogonal sequences available for synchronization is reduced since some are necessary for the data.

[0127] To summarize, the continuous synchronization approach described here provides a lot of advantages over conventional concepts.

[0128] However, in some embodiments according to the invention, a different synchronization concept may apply.

4.2. 2D propagation

[0129] Some modalities of the proposed system carry out propagation in both time and frequency domain, that is, two-dimensional propagation (briefly designated as 2D propagation). It has been found that this is advantageous with respect to ID systems since the proportion of erroneous bits can be further reduced by adding redundancy for example in time domain.

[0130] However, in some embodiments according to the invention, a different propagation concept may be applied.

4.3. Differential Coding and Differential Decoding

[0131] In some embodiments according to the invention, increased robustness against movement and inequality or frequency incompatibility of local oscillators (when compared with conventional systems) is achieved by differential modulation. It has been found that in fact, the Doppler effect (movement) and frequency inequalities lead to a rotation of the BPSK constellation (in other words, a rotation in the complex plane of the bits). In some embodiments, the harmful effects of this rotation of the BPSK constellation (or any other appropriate modulation constellation) are avoided by using differential coding or differential decoding.

[0132] However, in some embodiments according to the invention, a different coding concept or decoding concept may apply. Also, in some cases, differential coding may be omitted.

4.4. Bit shaping

[0133] In some embodiments according to the invention, bit shaping achieves a significant improvement in system performance, because the reliability of the detection can be increased using a filter adapted to bit shaping.

[0134] According to some modalities, the use of bit shaping with respect to digital watermark application results in improved reliability of the digital watermark application process. It has been found that particularly good results can be obtained if the bit shaping function is longer than the bit range.

[0135] However, in some embodiments according to the invention, a different bit shaping concept may apply. Also, in some cases, bit shaping can be omitted.

4.5. Interactive between Psychoacoustic Model (PAM) and synthesis of Filter Bank (FB) [0136] In some modalities, the psychoacoustic model interacts with the modulator to fine tune the amplitudes that multiply the bits.

[0137] However, in some other modalities, this interaction may be omitted.

4.6. Preview and backward view features

[0138] In some modalities, "back view" and "preview" approaches are applied.

[0139] These concepts will be briefly summarized below. When a message is decoded correctly, synchronization is considered to have been achieved. Considering that the user is not jumping (zapping), in some modalities, a backward view is made in time and attempts are made to decode past messages (if they are not already decoded) using the same synchronization point (backward view approach) . This is particularly useful when the system starts.

[01140] In bad conditions, it can take 2 messages to achieve synchronization. In this case, the first message has no possibility in conventional systems. With the back view option, which is used in some embodiments of the invention, it is possible to save (or decode) "good" messages that have not been received only due to backward synchronization.

[0141] The preview is the same but it works towards the future. If I will have a message now, I know where my next message will be, and I can try to decode it in any way. Accordingly, overlay messages can be decoded.

[0142] However, in some embodiments according to the invention, the preview feature and / or the back view feature may be omitted.

4.7. Increased synchronization robustness

[0143] In some modes, to obtain a robust synchronization signal, synchronization is performed in partial message synchronization mode with short synchronization signatures. For this reason, many decodes must be performed, increasing the risk of false positive message detections. To avoid this, in some embodiments, signaling sequences can be inserted into messages with a lower bit rate as a consequence.

[0144] However, in some embodiments according to the invention, a different concept may be applied to improve the robustness of synchronization. Also, in some cases, the use of any concepts to increase the robustness of synchronization can be omitted.

4.8. Other improvements

[0145] Next, some other general improvements of the system described above with respect to the prior art will be presented and discussed:

one.

 Less computational complexity

2.

 Better audio quality due to better psychoacoustic model

3.

 More robustness in reverberant environments due to narrowband multi-carrier signals

Four.

 An SNR estimate is avoided in some modalities. This allows for better robustness, especially in low SNR regimes.

[0146] Some embodiments according to the invention are better than conventional systems, which use very narrow bandwidths for example of 8 Hz for the following reasons:

one.

 8 Hz bandwidths (or similar very narrow bandwidth) require very long time symbols because the psychoacoustic model allows very little energy to make it inaudible;

2.

 8 Hz (or similar very narrow bandwidths) make time-sensitive Doppler spectra sensitive. Accordingly, this narrowband system is typically not good enough, if it is implemented for example in a clock.

[0147] Some modalities according to the invention are better than other technologies for the following reasons:

one.

 Techniques that feed an echo completely fail in reverberant rooms. In contrast, in some embodiments of the invention, the introduction of an echo is avoided.

2.

 Techniques that use only time propagation have a longer message duration compared to modalities of the system described above where a two-dimensional propagation is used, for example in both time and frequency.

[0148] Some modalities according to the invention are better than the system described in DE 196 40 814, because one or more of the following disadvantages of the system according to the document are overcome:

•

 the complexity in the decoder according to DE 196 40 814 is very high, a filter of length 2N with N = 128 is used.

•

The system according to DE 196 40 814 comprises a long message duration

•

in the system according to DE 196 40 814, propagation only in the time domain with relatively high propagation gain (for example 128)

•

In the system according to DE 196 40 814 the signal is generated in the time domain, transforms to the spectral domain, ponders, transforms back to time domain and overlays in audio, which makes the system very complex.

5. Applications

[0149] The invention comprises a method for modifying an audio signal to hide digital data and a corresponding decoder capable of retrieving this information while the perceived quality of the modified audio signal remains indistinguishable from the original.

[0150] Examples of possible applications of the invention are given below:

one.

 Broadcast supervision: information that contains a digital watermark for example at the station and time is hidden in the audio signal of radio or television programs. Decoders, incorporated in small devices that carry the test subjects, are able to recover the digital watermark, and in this way collect valuable information for advertising agencies, that is, who they see what program and when.

2.

 Audit: a digital watermark can be hidden for example in advertisements. By automatically monitoring the transmissions of a certain station it is then possible to know when exactly the announcement was broadcast. Similarly, it is possible to retrieve statistical information regarding the programming schedules of different radios, for example how often a piece of music is presented, etc.

3.

 Embedding metadata: the proposed method can be used to hide digital information regarding the program or piece of music, for example name and author of the piece or duration of the program, etc.

6. Implementation Alternatives

[0151] Although some aspects have been described in the context of an apparatus, it is clear that these aspects also represent a description of the corresponding method, wherein a block or device corresponds to a method stage or a characteristic of a method stage. Similarly, aspects described in the context of a method stage also represent a description of a corresponding block or item or characteristic of a corresponding apparatus. Some or all of the method steps can be executed by (or using) a physical equipment apparatus, for example a microprocessor, a programmable computer or an electronic circuit). In some embodiments, some or more of the most important method steps can be performed by this apparatus.

[0152] The encoded digital watermark signal of the invention, or an audio signal in which the digital watermark signal is embedded, may be stored in a digital storage medium or transmitted in such a transmission medium. as a wireless transmission medium or a wired transmission medium such as the Internet.

[0153] Depending on certain implementation requirements, modalities of the invention may be implemented in physical equipment or software. The implementation can be done using a digital storage medium, for example a floppy disk, a DVD, a Blue-Ray disc, a CD, a ROM, a PROM, an EPROM, an EEPROM or a FLASH memory, which has control signals electronically readable stored there, which cooperate (or are able to cooperate) with a programmable computer system such that the respective method is performed. Therefore, the digital storage medium can be computer readable.

[0154] Some embodiments according to the invention comprise a data carrier that has electronically readable control signals, which are capable of cooperating with a programmable computer system, such that one of the methods described herein is performed.

[0155] In general, embodiments of the present invention can be implemented as a computer program product with a program code, the program code is operative to perform one of the methods when the computer program product is executed in a computer. The program code can for example be stored in a machine-readable carrier carrier.

[0156] Other modalities include the computer program for performing one of the methods described herein, stored in a machine-readable carrier.

[0157] In other words, one embodiment of the method of the invention is therefore a computer program that has a program code to perform one of the methods described herein when the computer program is run on a computer.

[0158] A further embodiment of the methods of the invention is therefore a data carrier (or a digital storage medium, or a computer-readable medium) comprising, there recorded, the computer program for performing one of the methods described here.

[0159] A further embodiment of the method of the invention is therefore a data stream or a sequence of signals representing the computer program to perform one of the methods described herein. The data stream or the signal sequence can be configured, for example, to be transferred via a data communication connection, for example over the Internet.

[0160] An additional mode comprises processing means, for example a computer or a programmable logic device, configured for or adapted to perform or execute one of the methods described herein.

[0161] An additional mode comprises a computer that has the computer program installed there to perform one of the methods described herein.

[0162] In some embodiments, a programmable logic device (for example field programmable gate array) can be used to perform some or all of the functionalities of the methods described herein. In some embodiments, a programmable gate array can cooperate with a microprocessor in order to perform one of the methods described herein. In general, preference methods are performed by any physical equipment apparatus.

[0163] The modalities described above are only illustrative for the principles of the present invention. It is understood that modifications and variations of the arrangements and details described herein will be apparent to others with skill in the specialty. It is therefore intended that it be limited by the scope of the pending claims and not by specific details shown by way of description and explanation of these modalities.

Claims (15)

one.

 Watermark generator (101; 2400) for supplying a watermark signal (101b; 2420) based on binary message data (101a, m; 2410), the watermark generator comprising:

an information processor (303, 304, 305; 2430) configured to distribute binary message data to a plurality of frequency bands or frequency subbands and to deliver, depending on information units of the message data binary, a first representation in the temporal-frequency scope (b (ij); 2432) whose values represent the binary message data for a plurality of frequency bands or frequency subbands and temporal blocks, where b (i , j) is the bit for the ith frequency band or sub frequency band and the jth time block; and a differential encoder (306; 2440) configured to derive a second representation in the time-frequency scope (306a, bdiff (i, j); 2442) from the first representation in the time-frequency field, so that the second representation in the temporal-frequency scope it comprises a plurality of values, where a bdiff value (i, j) of the second representation in the temporal-frequency scope is a function of a bdiff value (i, j-1) of the second representation in the temporal-frequency scope and a value b (i, j) of the first representation in the temporal-frequency scope and where a difference between two values (bdiff (i, j), bdiff (i, j-1)) of the Second representation in the temporal-frequency scope represents a corresponding value of the first representation in the temporal-frequency field, to obtain a differential coding of the values of the first representation in the temporal-frequency field; and a watermark signal provider (307; 2450) configured to deliver the watermark signal based on the second representation in the time-frequency scope.

2.

 Watermark generator according to claim 1, wherein the information processor is configured to provide the first representation in the time-frequency scope so that the values of the first representation in the time-frequency field represent the message data binaries present in the form of a propagated binary model; and in which the differential encoder is configured to derive the second representation in the time-frequency scope so that a phase change between two successive values of the second representation in the time-frequency field is introduced if a corresponding value of the first representation in the temporal-frequency scope adopts a first value and so that there is no change of value between two successive values of the second representation in the temporal-frequency field if a corresponding value of the first representation in the temporal-frequency field adopts a second value that is different from the first value.

3.

 Watermark generator according to claim 2, wherein the information processor is configured to provide a bdiff bit value (i, j-1), associated with the ith frequency band and the jth block

where bdiff (i, j-1) designates a bit value associated with the i-th frequency band and the j-1-th time block of the second representation in the time-frequency scope; where b (i, j) designates a bit value associated with the ith frequency band and the jth time block of the first representation in the frequency temporal scope; and where the binary states of the first representation in the temporal-frequency scope are represented by the values +1 and -1.

Four.

 Watermark generator according to any one of claims 1 to 3, wherein the watermark signal provider is configured to deliver a combined audio signal (107) based on the second representation in the time-frequency scope, so that a watermark component of the watermark signal comprises a phased or smooth phase change in response to a first value of the first time-frequency scope representation, and so that the mark frequency component of water of the watermark signal comprises a constant phase in time in response to a second value of the first representation in the time-frequency scope that is different from the first value.

5.

 Watermark generator according to any one of claims 1 to 4, wherein the supplier of the watermark signal is configured to supply a first bit-forming waveform (giT (t)) in response to a first value of the second representation in the temporal-frequency domain, and to provide a second bit-forming waveform (-gi T (t)) in response to a second value of the second representation in the temporal-frequency domain, and in which the watermark signal provider is configured to include in the watermark signal a weighted or unweighted overlap of time-shifted versions of the same bit formation waveform in response to the presence of a first value in the first representation in the frequency temporal scope, and to include in the watermark signal a weighted or unweighted overlap of versions displaced in time of the first for The bit formation waveform and the second bit formation waveform in response to the second value that is different from the first value in the first time-frequency domain representation.

6.

 Watermark generator according to claim 5, wherein the second bit formation waveform is the inverse of the first bit formation waveform.

7.

 Watermark decoder (200; 2500) for supplying binary message data (202a; 2520) based on a watermark signal (200a; 2520), the watermark decoder comprising:

a representation provider in the temporal-frequency scope (1600; 2530) configured to provide a first representation in the temporal-frequency scope (bi norm (j); 2532) of the watermark signal, where the bi norm values ( j) of the first representation in the temporal-frequency scope include information about the phase of signal components at the fi frequency and at the moment j; a differential decoder (1608; 2540) configured to derive a second representation in the time-frequency scope (bi (j); 2542) from the first representation in the time-frequency scope, so that the values of the second representation in the temporal-frequency scope are a function of phase differences between two corresponding values (bi norm (j), bi norm (j-1)) of the first representation in the temporal-frequency field; and a synchronization determiner (201; 2550) configured to obtain synchronization information (205; 2552) based on the second representation in the time-frequency scope; and a watermark extractor (202; 2560) configured to extract the binary message data of the first time-frequency representation of the watermark signal or the second representation in the time-frequency field of the Watermark signal with the help of synchronization information.

8.

 Watermark decoder (200; 2600) to provide binary message data (202a; 2620) based on a watermark signal (200a; 2610), the watermark decoder comprising:

a representation provider in the temporal-frequency scope (1600; 2630) configured to provide a first representation in the temporal-frequency scope (bi norm (j); 2632) of the watermark signal, where the bi norm values ( j) of the first representation in the temporal-frequency scope include information about the phase of signal components at the fi frequency and at the moment j; a differential decoder (1608; 2640) configured to derive a second representation in the temporal-frequency scope (bi (j); 2542) from the first representation in the temporal-frequency scope, so that the values of the second representation in the temporal-frequency scope are a function of phase differences between two corresponding values (bi norm (j), bi norm (j-1)) of the first representation in the temporal-frequency field; and a watermark extractor (202; 2650) configured to extract the binary message data of the second representation in the time-frequency scope.

9.

 Watermark decoder according to claim 7 or claim 8, wherein the time-frequency scope representation provider is configured to supply, for a plurality of bands

norm of frequencies and for a plurality of time intervals, soft bit coefficients (bi AFB (j), (bi (j)) describing an amplitude and phase of the watermark signal in the frequency bands and intervals of time, and in which the differential decoder is configured to determine a value (bi (j)) of the second representation in the temporal-frequency scope associated with a given frequency band (fi) and a time interval (j ) given based on two corresponding values (bi norm (j), (bi norm (j-1)) of the first representation in the temporal-frequency scope.

10.

 Watermark decoder according to any one of claims 7 to 9, wherein the watermark decoder comprises an analysis filter (1600) configured to convolve the watermark signal or a mixed down version of the latter with a first bit formation function (giR (t)); and in which the watermark decoder is configured to sample in time a result of the convolution, to obtain discrete values at the time of the first representation in the temporal frequency field; and when the watermark decoder is configured to adjust a time order used for sampling the convolution result at a sub-bit interval resolution based on synchronization information, to maximize a signal-to-noise ratio and to minimize a symbol interference ratio.

eleven.

 Watermark decoder according to any of claims 7 to 10, wherein the differential decoder is configured to derive the second representation in the time-frequency scope independently for the different frequency bands (fi), so that different rotations of Watermark signal phase in different frequency bands be compensated independently by the differential decoder; and in which the synchronization determiner or the watermark detector is configured to jointly treat a set of values of the second representation in the time-frequency scope associated with

a certain part of time and different frequency bands, to obtain a synchronization information or a bit of the binary message data.

12.

 Portable watermark evaluation device (2700), comprising:

a microphone (2710) configured to supply an electric microphone signal (2712); and a watermark decoder (2720) according to any one of claims 7 to 11, wherein the watermark decoder is configured to receive a microphone signal as a watermark signal.

13.

 Procedure (2800) for supplying a watermark signal based on binary message data, the procedure comprising:

distribute the binary message data to a plurality of frequency bands or frequency subbands, to provide (2810), based on information units of the binary message data, a first representation in the temporal-frequency domain b ( i, j), whose values represent the binary message data for a plurality of frequency bands or frequency subbands and time blocks, where b (i, j) is the bit for the ith frequency band or sub -frequency band and the j-th time block; derive (2820) a second representation in the temporal-frequency scope of the first representation in the temporal-frequency scope, so that the second representation in the temporal-frequency scope comprises a plurality of values, where a bdiff value (i, j) of the second representation in the temporal-frequency scope is a function of a bdiff value (i, j-1) of the second representation in the temporal-frequency scope and of a b (i, j) value of the first representation in the temporal scope -frequential and where a difference between two values of the second representation in the time-frequency scope represents a corresponding value of the first representation in the time-frequency field, to obtain a differential coding of the values of the first representation in the time-frequency field ; and supply (2830) the watermark signal based on the second representation in the time-frequency scope.

14.

 Procedure (2900) for supplying binary message data based on a watermark signal, the procedure comprising:

supply (2910) a first representation in the temporal-frequency scope of the watermark signal where the bi norm (j) values of the first representation in the temporal-frequency scope comprise information about the phase of signal components at the frequency fi and at time j; derive (2920) a second representation in the time-frequency scope of the first representation in the time-frequency scope, so that the values of the second representation in the time-frequency scope are a function of phase differences between two corresponding values of the first representation in the temporal-frequency scope; and using (2930) the second representation in the time-frequency scope to determine a synchronization information that is used to supply the binary message data, or to extract the binary message data from the watermark signal.

fifteen.

 Computer program adapted to perform the method according to claim 13 or claim 14, when the computer program is run on a computer.